Ethylene oxide is typically prepared by catalytic oxidation of ethylene with oxygen. Metallic silver carried on an inert support material is typically employed as catalyst, the catalyst typically containing promoting amounts of other additives, for example, alkali metals or alkaline earth metals.
Such catalysts are typically prepared by impregnating the support material with a solution of silver compound followed by heating in the presence of a reducing agent to convert the silver compound to metallic silver. The reducing agent is usually a constituent of the impregnating solution and is deposited on the support material along with the catalytic actives, the reducing agent being volatized in the subsequent heating step.
The reducing agents are typically nitrogen containing organic compounds such as, for example, alkanol amines and alkylene diamines. According to U.S. Pat. No. 3,962,136 a combination of ethylene diamine with ethanolamine is most preferred as a reducing agent. However, ethylene diamine can coordinate with silver in either a monodentate or bidentate mode and monoethanolamine can compete with ethylene diamine for coordination sites, with the result that a mixture of complexes having different component ratios can be formed, which could result in variations in the effectiveness of reduction of silver complex to silver metal with the consequence that catalytic activity and selectivity could vary from catalyst to catalyst.
Since in the production of ethylene oxide by catalytic oxidation of ethylene with oxygen the overall economics of the process are very sensitive to raw materials cost catalytic selectivity is extremely important and even relatively small variations in selectivity are crucial from the standpoint of operations economics.